Sponges from the Atlantic Ocean. 227 



/a/TCrt occa, &c., from tlie same source, were described [op.cit. 

 vol. xii. ]». 44')). After tliis several of these sponges were 

 described and ilhistrated in 1S74 (o/>. cit. vol. xiv. p. 207i^'e.); 

 and now 1 have to offer the remainder, — dredged up on board 

 the ' rorcuj)ine ' in 18G9 and 1870. 



As regards the form and measurements of sponges, whether 

 entire or fragmentary, and as regards that of their s])icules, 

 nothing can be more variable. They all grow from small to 

 large, and all may vdvy more or le^s in every respect during 

 the course of their development ; so that what I have stated in 

 this paper must be understood to be what the sponges dredged 

 up on board the ' Porcupine ' only, present. 



Thus, then, as the spicules in particular grow from small to 

 large, and are successively developed, they Avill be found to 

 be of all sizes in the sponge to which they may belong. Hence 

 their average largest size resj)ectively has been taken for 

 description, measurement, and illustration. 



The measurements are all in parts of an inch ; and for the 

 convenience of the student they are given in accordance with 

 the divisions of my micrometer eye-piece, viz. in ISOOths or 

 6000ths of an inch, under a magnifying-power approximately 

 of 85 and 206 diameters ; while for the detail other powers 

 (of 120 and 375 approximately) have been employed. 



As the numbers alone are given in the descriptions, they 

 must be understood to refer to the greatest diameters of the 

 average largest size of the spicule, without this being expressed. 

 Thus the description of an acerate or linear form may have 

 appended to it, " 100-1800ths by 2-1800ths inch," which 

 means 100-1800ths inch long and 2-1800ths inch broad in 

 its greatest diameters. By this the student will at once be able 

 to draw the spicule to any scale ; or if he chooses to reduce 

 the fractions to their ultimate value, — he would gQ,i in this 

 instance l-18th by 1 -900th inch. 



Again, a spicule may be attenuatingly or abruptly pointed — 

 that is, drawn out gradually to a sharp point or abru])tly termi- 

 nating in one which, if altogether omitted, would give a round 

 end. This is the meaning of these expressions. 



Lastly, as regards colour. It should be remembered that 

 all the specimens have come to me in spirit or dry respectively, 

 and therefore that, as the colours of sponges are in some in- 

 stances ])ermanent and in others evanescent, I can onlv give 

 that colour which these sponges vow present to me. Aphjsina 

 ncevus still retains its dark red-purple tint ; but most of the rest 

 present different shades of what may be termed " sponge- 

 colour," viz. tawny, light yellow, grey, or whitish ; at the 

 same time, these arc the colours which sponges usually have. 



